This invention relates to an apparatus for applying viscous substances, for example adhesives to the frame flanges of window openings in motor vehicles. In the construction of automobiles, recently window panes have frequently been bonded to the frame flanges of window openings, instead of being inserted in rubber packings. This has safety advantages, because a bonded window pane will less readily fall out of the window in the case of an accident, than a pane which is fitted therein. In addition, bonded window frames additionally reinforce the body and reduce air resistance.
For bonding window panes to the window flanges the procedure has hitherto been to manually apply an all-round adhesive bead by means of an applicator, after which the pane with the adhesive bead is pressed onto the frame flange in the window opening. However, this takes a relatively large amount of time and requires high concentration and considerable skill from the worker to ensure that the adhesive bead is always uniformly applied and subsequently the pane is accurately fitted into the window opening.
From the assembly standpoint, it would be ideal to have an apparatus enabling the adhesive bead to be applied to the frame flange of the window opening instead of to the pane, because it is easier to handle the pane without adhesive and to introduce it into the correct position with respect to the window opening. However, it has hitherto proved impossible to develop an automatic apparatus for applying adhesive to a frame flange, owing to the necessary high accuracy of the adhesive quantity applied and the necessary exact positioning of the adhesive bead on the frame flange.
The main problem to be solved with such an apparatus is that the frame flange of the window opening is not suitable for supporting and guiding a discharging device, because it has too small an area, frequently too abrupt deflections in the corners and through being painted is too smooth, in order to produce e.g. by means of a friction wheel an accurate and uniform feed speed of the applicator on the path thereof. If, for example, a guide wheel were to be placed on the window frame and said wheel was allowed to determine the feed speed of the discharging device, the speed of the latter in the corners would be much less than in the straight areas, because the discharge nozzle is closer to the centre of curvature in the corners than the guide wheel and would therefore have to cover less distance in taking a curve than would the guide wheel. As a result, more adhesive would be applied to the corner areas than in the straight areas of the frame flanges. On inserting the window pane, this adhesive would then flow out of the corners, giving an unattractive appearance and impeding the insertion of a decorative strip between the outer edge of the window pane and the window frame.